This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Protein crystallography is a great tool for elucidating macromolecular structures at near atomic resolution and it is considered the most dominant technique for structure determination as evidenced by the number of deposited structures in PDB using this method. However, like any other techniques, protein crystallography cannot go without a limit and it is bound by the requirement for high quality crystals. Membrane proteins represent over 25% of all eukaryotic genome sequences and are difficult to crystallize. Similar situations exist for proteins that exhibit extensive conformational changes necessary for function. Here, we used SAXS to study a few selected membrane proteins and an AAA ATPase whose conformational changes is a prerequisite for function.